I wouldn't look at this color yellow as garish but as bright and cheerful, appropriate for a young boy. Are you saying the other tractor prints that are in a directional print are for the backing, or are they for other blocks? If the other tractor prints aren't for the other blocks, then I would suggest you make the other blocks something a boy would be interested in: animal prints, sport prints, other vehicles. What boy would be interested in a pinwheel block? Think about when the boy is sick in bed, what will he like looking at on this quilt? When he is laying on his quilt daydreaming, what will he see in different areas on his quilt? It should be more than a bed covering when it is for a young boy.